The operating speed and other functions of a conventional treadmill are controlled by a control panel provided by the treadmill, wherein the control panel is composed of a control mainboard, an input system, and a display system. When a user enters a command from the input system, the input system will immediately generate a signal, which will be transmitted to a motor of the treadmill through the control mainboard so as to control the operating speed of the treadmill. In the meantime, the signal will be transmitted to the display system of the treadmill for the user's reference.
However, the control mainboard, the input system and the display system are together fixedly mounted on the control panel of the conventional treadmill to make the control panel function normally. Additionally, the control mainboard is manufactured along with the treadmill and is exclusively made for structurally corresponding to the treadmill. Therefore, the control mainboard of the treadmill cannot be recycled for other types of treadmills. Furthermore, the aforesaid control mainboard is expensive and there are commercially many types of treadmills, which will soon be outdated and deserted. If the control mainboard is exclusively used in one treadmill, once the treadmill is outdated and deserted, the control mainboard will be synchronically deserted and cannot be recycled. As a result, it's wasteful and the production cost of new treadmills will be relatively increased.